To produce hydrocarbons from a subterranean reservoir, one or more wellbores are drilled through the earth formation to the reservoir. Each wellbore is then completed by installing casing or liner sections and by installing production tubing, packers, and other downhole components. For certain types of wells, artificial lift systems are installed to enhance the production of hydrocarbons. One such artificial lift system includes an electrical submersible pump that pumps fluids from a downhole location in a wellbore to the well surface. Another type of artificial lift system is a gas lift system, where pressurized gas (pumped from the surface of the well or from an adjacent wellbore) is used to lift well fluids from a downhole location in the wellbore.
Yet another type of artificial lift mechanism is a plunger lift production mechanism often used to remove oil or other liquids from gas wells. Gas wells that require swabbing, soaping, blowing down, or stop cocking are candidates for plunger lift production mechanisms. A plunger lift production mechanism typically includes a relatively small cylindrical plunger that travels through tubing extending from a downhole location adjacent a producing reservoir to surface equipment located at the open end of the wellbore. In general, liquids that collect in the wellbore and inhibit the flow of gas out of the reservoir and into the wellbore are collected in the tubing. Periodically, the end of the tubing is opened at the surface and the accumulated reservoir pressure is sufficient to force the plunger up the tubing. The plunger carries with it to the surface a load of accumulated fluids that are ejected out of the top of the well to allow gas to flow more freely from the reservoir into the wellbore and to a distribution system at the well surface. After the flow of gas has again become restricted due to further accumulation of fluids downhole, a valve in the tubing at the well surface is closed so that the plunger falls back down the tubing for lifting another load of fluids to the well surface upon reopening of the valve.
In plunger lift production mechanisms, there is a requirement for the periodic operation of a motor valve at the wellhead to control the flow of fluids from the well to assist in the production of gas and liquids from the well. Conventionally, a motor valve is controlled by a timing mechanism that is programmed in accordance with principles of reservoir engineering to determine the length of time that the well should either be “shut in” (and restricted from flowing) and a time the well should be “opened” to freely produce. Generally, the criterion used for operation of the motor valve is strictly based on a pre-selected time period. In most cases, parameters such as well pressure, temperature, and so forth, are not available in conventional plunger lift production mechanisms because of the costs associated with intervention to obtain well pressure, temperature, and other information.
Operation of a motor valve based only on time is often not adequate to control outflow from the well to enhance well production. Proper setting of logic to control the plunger lift production mechanisms usually is based on trial and error, with continued evaluation needed for changing well performance that necessitates well site trips to adjust timing for the control of motor valves.